Abstract
Abstract We present high-resolution (submas) Very Long Baseline Interferometry maps of nuclear H2O megamasers for seven galaxies. In UGC 6093, the well-aligned systemic masers and high-velocity masers originate in an edge-on, flat disk and we determine the mass of the central supermassive black holes (SMBH) to be M SMBH = 2.58 × 107 M ⊙ (±7%). For J1346+5228, the distribution of masers is consistent with a disk, but the faint high-velocity masers are only marginally detected, and we constrain the mass of the SMBH to be in the range (1.5–2.0) × 107 M ⊙. The origin of the masers in Mrk 1210 is less clear, as the systemic and high-velocity masers are misaligned and show a disorganized velocity structure. We present one possible model in which the masers originate in a tilted, warped disk, but we do not rule out the possibility of other explanations including outflow masers. In NGC 6926, we detect a set of redshifted masers, clustered within a parsec of each other, and a single blueshifted maser about 4.4 pc away, an offset that would be unusually large for a maser disk system. Nevertheless, if it is a disk system, we estimate the enclosed mass to be M SMBH < 4.8 × 107 M ⊙. For NGC 5793, we detect redshifted masers spaced about 1.4 pc from a clustered set of blueshifted features. The orientation of the structure supports a disk scenario as suggested by Hagiwara et al. We estimate the enclosed mass to be M SMBH < 1.3 × 107 M ⊙. For NGC 2824 and J0350−0127, the masers may be associated with parsec- or subparsec-scale jets or outflows.
Highlights
H2O megamasers are found in high-density, warm molecular gas with a large water abundance in the central parsec of galaxies with Seyfert 2 or LINER spectra, either in the circumnuclear disks, or associated with the jets and outflows triggered by these active galactic nuclei (AGNs)
We present Very Long Baseline Interferometry (VLBI) maps of H2O megamasers for seven active galaxies, six for the first time
The H2O megamaser in UGC 6093 clearly originates in a circumnuclear disk orbiting a supermassive black holes (SMBHs) of mass MSMBH = 2.58 × 107M⊙ (±7%)
Summary
H2O megamasers are found in high-density, warm molecular gas with a large water abundance in the central parsec of galaxies with Seyfert 2 or LINER spectra, either in the circumnuclear disks, or associated with the jets and outflows triggered by these active galactic nuclei (AGNs). VLBI can resolve the gravitational “sphere of influence” of the SMBH in many megamaser disks, and the mass can be measured accurately when the rotation of the edge-on disk is observed to be Keplerian. To date, with this method, 20 SMBH masses have been measured (e.g. Greenhill et al 1996; Herrnstein et al 1999; Greenhill et al 2003; Kondratko et al 2005, 2008; Reid et al 2009; Kuo et al 2011; Yamauchi et al 2012; Gao et al 2016; Greene et al 2016a; Gao et al 2017.) Most of the measured values are between 106 and a few times of 107M⊙, and the extremely high mass densities (ρ 1011M⊙ pc−3) inside the maser disks argue strongly against alternatives to SMBHs (e.g., a dense cluster of stars or stellar remnants) as the central objects in these galaxies. Components, but their VLBI maps reveal complex geometries and disordered dynamics In these cases, SMBH masses can not be determined by fitting a Keplerian rotation curve.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
